With the term hub we generically mean the assembly of a hub body inside which a shaft is rotatably coupled through its ends to the bicycle frame; the hub body is joined to the rim of the wheel through a plurality of spokes and rotates integrally with it.
With the term “direction” referring to a spoke attachment hole we mean the main direction according to which such a hole extends through the hub body; such a direction is the one according to which a perforating tool shall ideally be arranged in the case in which the hole is made by chip removal; it is also the direction according to which the longitudinal axis of a portion of a spoke or of a spoke attachment element (for example a nipple) engaged in such a hole is arranged.
With the expression “substantially parallel to a rotation axis of the hub body” we mean a direction that differs from that of the rotation axis of the hub body (or in short of the hub) by an angle equal to zero or in any case a very small angle, not greater than 10°, thus in such a way that the portion of spoke or of spoke attachment element engaged in such a hole is substantially perpendicular to the main portion of the spoke itself.
Hubs of this type are known and widely used in racing bicycles.
In other types of wheels, the type of hub body used is, on the other hand, that in which the direction of the spoke attachment holes is substantially radial with respect to the rotation axis of the hub, and therefore the portion of spoke or of spoke attachment element engaged in such a hole is substantially aligned with the main portion of the spoke itself. This type normally allows better control of the stresses in the spokes and therefore more accurate and careful sizing with respect to structural resistance, weight and to aerodynamic resistance during rolling of the wheel.
A known hub body of this type is known, for example, in which the tubular central portion of the hub body extends along a main rotation axis and has spoke attachment parts at its ends consisting of protrusions distributed circumferentially (four protrusions for each end). In each protrusion a pair of spoke attachment holes is made, to receive the heads of two spokes, or to receive two attachment nipples at the threaded heads of the spokes; each hole has its axis belonging to a plane substantially perpendicular to the main rotation axis of the hub.
In a first group of solutions, the two holes of each pair have their axes offset with respect to each other both in the radial direction and in the axial direction, with reference to the main rotation axis of the hub.
The different axial positioning of the holes along the main axis determines a disadvantageous assembly configuration of the spokes that have two different inclinations (cambers) with respect to the middle plane of the wheel passing through the rim.
A second solution overcomes the drawback of the different cambers of the spokes since the two holes of each pair belong to the same plane perpendicular to the main axis of the hub and are therefore axially aligned.
To satisfy particular requirements, for example for aesthetic reasons or else to increase the number of spokes, it is sometimes necessary to increase the number of spoke attachment holes distributing them circumferentially in groups of three or more holes.
The addition of one or more holes in the aforementioned protrusion containing the pair of axially aligned holes would require increasing the radial size of the protrusion itself to allow the further holes to be made. Moreover, the increase in the number of spokes associated with each protrusion increases the size of the flexing forces acting upon the protrusion requiring that it be widened so as to be able to ensure sufficient structural strength. The increase in the radial size of the protrusions and their thickening means an increase in weight of the hub body and greater aerodynamic resistance during movement.
Hub bodies in which axial spoke attachment holes are provided that are arranged on more than one circumference are not known.
There is therefore the problem of making a hub body that allows greater freedom in the arrangement of the spokes, in particular that allows the spoke attachment holes to be grouped into groups of three or more holes, and that at the same time can ensure low size and weight compared to known hubs.